Living polymerization was discovered in the 1950's of last century. It was first demonstrated by Michael Szwarc in 1956 in the anionic polymerization of styrene with an alkali metal/naphthalene system in tetrahydrofuran (THF). Szwarc found that, after addition of monomer to the initiator system, an increase in viscosity would eventually cease but that, the viscosity would start to increase again after addition of a new amount of monomer (en.wikipedia.org/wiki/Living polymerization). Since then, living polymerization has evolved and, in many laboratories around the world, conditions for obtaining such polymerization were discovered for various other types of anionic, cationic, ring-opening and free radical systems. Protection of the living end of a polymer from termination has been accomplished by complexation or by steric hindrance and by appropriate choice of reagents and solvents (Moshe Levy: “Living Polymers”—50 years of evolution).
Recently, U.S. Pat. No. 8,222,346 to Cao et al. disclosed a novel block copolymer, based on living polymerization, containing a controlled distribution of a conjugated diene and a mono alkenyl arene in copolymer blocks. Cao et al. disclosed, in a representative synthetic method, that an initiator compound can be used to start the polymerization of a first monomer. According to this method, the reaction is allowed to proceed until all of the monomer is consumed, resulting in a living homopolymer. To this living homopolymer is then added a second monomer that is chemically different from the first monomer. The living end of the first polymer serves as the site for continued polymerization, thereby incorporating the second monomer as a distinct block into the linear polymer. The block copolymer so grown is living until terminated (col. 1, line 16-26).
Various block copolymers have been prepared by cationic, group transfer, metallocence, and metathesis routes. This includes atom transfer radical polymerization (ATRP), nitroxide-mediated polymerization (NMP), and reversible addition-fragmentation chain transfer polymerization (RAFT). The significant advance in block and graft copolymer synthesis has come about with the advent of controlled radical polymerization (CRP) techniques (Handbook of Vinyl Polymers, Radical Polymerization, Process, and Technology; Second Addition, Edited by Mishra, et al, CRC Press; 2009).
On a different subject, glycine and its derivatives are organic compounds that have been used as free radical initiators in the polymerization of ethylenically unsaturated monomers, especially as photo-polymerization initiators. For example, U.S. Pat. No. 3,479,185 discloses the use of a system comprising N-phenyl glycine or N,N,N′,N′-ethylenediamino tetraacetic acid in combination with a 2,4,5-triphenylimidazolyl dimer as a photopolymerization catalyst system.
U.S. Pat. No. 4,058,656 to Markiewitz, et al, discloses a polymerizable system susceptible to free radical polymerization that comprises one or more ethylenically unsaturated compounds and, as an initiator, N-phenyl glycine or a derivative, wherein the initiator will yield a dissolved initiator compound upon acidification, provided that the ethylenically unsaturated compounds do not contain any group with which the acid group of the initiator compound will preferentially react. Markiewitz demonstrated solution polymerization in which polymerization, which occurred over several days in the presence of solvent or water, comprised dissolution and acidification of the initiator in the polymerization system. Markiewitz, however, made no mention of obtaining “living” polymerized materials.
Dental bonding systems utilizing N-phenyl glycine or its derivative compounds as a dentin surface bonding promoter, among other additives, are well known in dentistry. The use of such bonding systems principally follow the techniques outlined in U.S. Pat. Nos. 4,659,751 and 5,401,783, both to R. L. Bowen. To Applicant's knowledge, however, no “living” property has been associated with, or mentioned with respect to, such bonding systems.
On still another subject, organic compounds containing sulfonic acid groups or its alkali salts have been employed as photoinitiators in combination with dissolved chloride ions from a chloride compound, particularly in a process of polymerization using ultraviolet radiation (U.S. Pat. No. 4,105,519 to Pennewisse, et al.). Also, U.S. Pat. No. 5,520,725 to Kato et al. discloses a dental glass ionomer composition comprising (a) an α-β unsaturated carboxylic acid polymer having a weight-average molecular weight lying in a specific range, (b) a polymerizable unsaturated organic compound having a CH2═C(R1)—COO group, (c) water, (d) an organic aromatic compound having an —SO2 group, (e) a fluoroaluminosilicate glass powder having a mean particle size and specific gravity each lying in a specific range and capable of reacting with the component (a), and (f) a compound containing at least one element selected from the group consisting of aluminum, iron and tin. This composition can be cured either without recourse to conventional redox reaction systems or without exposure to visible light (Abstract and claim 1.) U.S. Pat. No. 6,730,715 to Jia also discloses the use of a sodium salt of bezenesulfinic acid in a dental composition.